Patent literature 1: JP 2006-27315 A
For example, Patent literature 1 discloses a configuration for reducing a common mode current at the time of using an electrically-driven compressor including an electric motor in an air-conditioner for a vehicle.
Since a portion between an electric motor and a motor housing is coupled through a stray capacity, when potential of the electric motor changes according to a switching operation of a motor controller (also referred to as a motor drive circuit), a current may leak from the electric motor to the motor housing. Due to this leakage current, an electric field noise may occur when the potential of the motor housing changes. In order to suppress the electric field noise, it may be effective to connect the motor housing with a body of a vehicle (also referred to as a vehicle body) to perform a body earth.
However, when the body earth of the motor housing is performed, and when a current route where the common mode current flows becomes a large loop through earth, a noise reduction effect may be reduced since intensity of an electric field noise is correlated with a loop area.
In order to reduce the noise by the common mode current, Patent literature 1 uses the following configuration. A motor controller is united with the electric compressor to provide a common housing, that is the motor controller and the electric compressor are provided integrally. The common housing is connected to a conductive film (corresponding to a sheath portion) of a shield wire having two core wires as a power source line and an earth line. The sheath portion of the shield wire is grounded to a body of the vehicle, and impedance in the earth route is set to large impedance to an extent that a leakage current does not generate an electric shock.
Since the impedance between the sheath portion and the vehicle body has a relatively large value, the current leaked to the vehicle body among the leakage current leaked to the common housing is reduced, and the remaining leakage current transmits to the core wire portion through the stray capacity between the sheath portion and the core wire portion to return (be refluxed) to the motor controller. According to this configuration, a magnitude of the loop of the common mode current is reduced, so that the noise is suppressed.
The inventors of the present disclosure have found the following. Patent literature 1 merely discloses a configuration for reducing the noise in a mechanically and electrically integrated apparatus in which the electric motor and the motor controller are integrated. However, it may be necessary to use a configuration having an electric motor and a motor controller as a different body (that is, separately) according to, for example, an ambient condition on which an electric motor is used.